小型二冲程汽油机缸内工作过程模拟

本文建立了用于小型二冲程汽油机的缸内工作过程计算模型,应用理论计算方法对缸内工作过程进行了较为详尽的描述,计算结果与试验结果基本吻合,为小型二冲程汽油机的设计提供了较好的依据     

小型四冲程汽油机准维循环模拟研究

汽油机循环模拟以建立汽油机一个完整循环过程的数学模型为基础,它可用来研究流动、传热和燃烧等过程的细节及发动机整机性能。本模拟把运行模式、运行工况、气道状态、传热、湍流参数及发动机设计等参数作为输入,输出不同曲轴转角下的气缸压力、温度、传热率和通过进、排气门的工质质量流量、流速及燃烧阶段卷吸燃烧质量百分数。循环结束后,给出积分结果,如容积效率、热效率、指示压力、平均有效压力、热损失、平均排气温度及油耗等。文中还通过对ＭＴ１００四冲程机的实例计算,证明了模拟的实用性。     

Experimental investigation of varying composition of HCNG on performance and combustion characteristics of a SI engine

With rapid depletion of petroleum resources, researchers are investigating alternate fuels to meet global transportation energy demand. Gaseous fuels such as compressed natural gas (CNG) and hydrogen are of special interest because of their cleaner combustion characteristics compared to liquid petroleum based fossil fuels. However both these gaseous fuels have some technical issues when they are used as stand-alone alternate fuel in conventional spark ignition (SI) engines. CNG suffers from lower energy density and narrow flammability range whereas backfiring tendency is highly pronounced in hydrogen fueled engines. Hydrogen enriched compressed natural gas (HCNG) mixtures are observed to be good alternative to these individual fuels since these mixtures do not pose the issues experienced by the constituent fuels i.e. CNG and hydrogen. In this study, experiments were conducted in a spark ignited gas engine using various compositions of HCNG mixtures having 0, 10, 20, 30, 50, 70 and 100% (v/v) hydrogen fraction. The performance and combustion characteristics of these test fuels were compared with that of baseline CNG, in order to find an optimum HCNG mixture composition for a single cylinder gas engine. Results obtained showed that 30HCNG mixture delivered superior engine performance compared to other HCNG mixtures and baseline CNG, which is in sharp contrast to 15HCNG being advocated globally.     

Estimating the charge burning velocity within a hydrogen-enriched gasoline engine

This paper proposed a feasible method for estimating the turbulent burning velocity of gasoline/hydrogen blends in a spark-ignited (SI) engine based on the cumulative heat release fraction, engine speed and engine geometry. The experiment was conducted on a naturally-aspirated port-injection gasoline engine equipped with a hydrogen injection system. The engine was run at 1400 rpm with different loads and hydrogen volume fractions in the intake gas. The test results showed that the addition of hydrogen benefited increasing the burning velocity and advancing the relevant crank angle for the peak burning velocity, due to the high burning and diffusion velocities of hydrogen. At 1400 rpm, a manifolds absolute pressure of 61.5 kPa and stoichiometric conditions, the peak burning velocity was raised from 11.6 to 12.3 and 14.6 m/s, and the relevant crank angle for the peak burning velocity was advanced from 21.0 to 14.0 and 8.6 ^oCA when the hydrogen volume fraction in the intake increased from 0% to 3% and 6%, respectively. Moreover, the effect of hydrogen addition on enhancing the burning velocity of a gasoline engine was more pronounced at low loads than that at high loads.     

Influence of high compression ratio and hydrogen addition on the performance and emissions of a lean burn spark ignition engine fueled by ethanol-gasoline

This paper investigates the effect of ethanol-gasoline-hydrogen in a lean-burn SI engine with different proportions such as E5, E10, E20, E30, and E40 at compression ratio 10.5:1. The results infer that the E10 blend is the optimized one. Further, E10 mixture investigates for 5% and 10% hydrogen addition on energy basis. Overall, this study establishes that the addition of ethanol enhances brake power by 9% and brake thermal efficiency by about 7%. Hydrogen enrichment to E10 mixture shows a significant enhancement in brake power and brake thermal efficiency at a lower equivalence ratio. Further, it observes that the lean limit had extended to a 0.47 equivalence ratio compared to a 0.5 equivalence ratio with the E10, and 0.54 with pure gasoline. The addition of hydrogen to E10, improves the combustion process and heat release rate while it reduces cycle-by-cycle variations and hydrocarbon emissions.     

钙离子光频标钟跃迁绝对频率测量

回顾了中国科学院精密测量科学与技术创新研究院对钙离子光频标钟跃迁绝对频率的测量工作，并对测量结果被国际计量委员会（CIPM）下属的时间频率咨询委员会（CCTF）采纳的情况进行了总结和描述。在2011～2020年间，利用实验室型光频标和可搬运光钟，采用基于飞秒光梳和卫星链路的方案溯源到国际秒定义，及基于飞秒光梳直接溯源到中国计量科学研究院铯喷泉微波钟的方案，多次测量了钙离子光频标钟跃迁绝对频率，测量不确定度从10^-15量级逐步提高到10^-16量级，共计4个测量结果被CCTF采纳。参与钙离子光频标钟跃迁频率国际推荐值的计算，分别于2012年、2015年、2017年和2021年先后四次更新了钙离子光频标钟跃迁频率推荐值。钙离子光频标钟跃迁于2021年被推荐为新增的“秒的次级表示”。     

Study of combustion and emission of a SI engine at various CR fuelled with different ratios of biobutanol/hydrogen fuel

The global requirement is shifting to territorial independence of energy sources, and the introduction of alcohols and biofuels are the primary sectors. Recently agriculture products-based ethanol has replaced a larger portion of gasoline. Butanol is another impressive fuel in the same chain, much better than ethanol in many parameters. Butanol has certain limitations, too, such as higher latent heat and low heating value. Therefore, biobutanol/hydrogen is tested experimentally at various compression ratios (CR) in the present study. Brake thermal efficiency was not significantly changed by CR at 90% butanol, while CR is more impressive with increasing hydrogen. The flame development period was reduced by 34%, while the flame propagation phase was reduced by 29% by increasing CR to 15 and hydrogen to 25%. Peak pressure and heat release rate surged by 12.89% and 12.32% and advanced by 6°CA. The coefficient of variations is also reduced by 21% by increasing CR to 15 and hydrogen to 30%. Higher hydrogen faced combustion difficulties due to increasing stratification and heterogeneity during combustion. Unlikely to trend, T_max (peak cylinder temperature) and NO_x were continuously increased with CR and hydrogen due to increased fuel quantity and larger mass burning before TDC. However, CO and HC emissions were reduced by CR due to increased BTE (brake thermal efficiency) and reduced by hydrogen due to less HC supply. A slight increase in HC and CO was noticed for higher hydrogen due to local heterogeneity and disassociation at high temperatures.     

Nickel-doped TiO2 and thiophene-naphthalenediimide copolymer based inorganic/organic nano-heterostructure for the enhanced photoelectrochemical urea oxidation reaction

To overcome the global challenges of energy crises and environmental threats, urea oxidation is a hopeful route to utilize urea-rich wastewater as an energy source for hydrogen production. Herein, we report an inorganic/organic type of nano-heterostructure (NHs–Ni-TiO₂/p-NDIHBT) as a photoanode with excellent urea oxidation efficiency driven by visible light. This heterostructured photoanode consists of nickel (Ni)-doped TiO₂ nanorods (NRs) arrays as an inorganic part and a D-A-D type organic polymer i.e p-NDIHBT as an organic part. The as-prepared photoanode was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The morphological studies of TEM confirm the coating of p-NDIHBT on Ni–TiO₂ NPs (～1 μm). The consequence of heterostructure formation on optical and photoelectrochemical (PEC) properties of photoanode were explored through photoelectrochemical responses under visible light irradiation. The photoelectrochemical activity of Ni–TiO₂ and Ni–TiO₂/p-NDIHBT photoanode from linear sweep voltammetry (LSV) shows the ultrahigh photocurrent density of 0.36 mA/cm² and 2.21 mA/cm², respectively measured at 1.965 V_RHE. Electrochemical impedance spectroscopy (EIS) of both photoanodes shows a highly sensitive nature toward the urea oxidation reaction. The hybrid photoanode also exhibits high photostability, good solar-to-hydrogen conversion efficiency, and high faradaic efficiency for urea oxidation.